1. Field of the Invention
The present invention relates to an optical-pickup device and a tilt-detecting method thereof.
2. Description of the Related Art
Recently, enlargement of the storage capacity of an optical recording medium, typically, an optical disc, is strongly demanded. In order to increase the storage capacity without enlargement of the size of the optical recording medium itself, it is necessary to reduce the diameter of the light spot used in information recording/reproducing. Because the diameter of the light spot is inversely proportional to the numerical aperture NA of the objective lens, the storage capacity is proportional to the square of the NA. Therefore, increasing the NA has been attempted. For example, an optical disc (DVD: Digital Versatile Disk) for performing recording/reproducing in a condition where NA=0.6 has been developed although a conventional optical disc (CD-RW: Compact Disk ReWritable) is such that recording/reproducing is performed in a condition in which NA=0.5.
In an optical-pickup device, rays from a light source are focused, so as to form a light spot, on a recording plane of an optical disc via a transparent substrate. The shape of the light spot is distorted due to coma occurring due to a tilt of the disc substrate. The coma is proportional to the cube of NA. Because setting is made such that NA=0.6 (larger) for the DVD while setting is made such that NA=0.5 for the CD-RW, the thickness of the substrate of the DVD is xc2xd of that of the CD so as to reduce the influence of coma. However, because various margins (the defocus, the control error and so forth) are reduced due to increase in the storage capacity, the allowable amount of the tilt of the disc substrate is small. In order to obtain the best RF signal by causing the objective lens of the optical pickup to face the optical disc in a condition where the axis of the objective lens is perpendicular to the disc substrate although the disc substrate tilts, it is necessary to perform tilt-servo control. In order to perform the tilt-servo control, a tilt sensor which detects the tilt of the disc substrate is needed.
An example of such a tilt sensor in the related art will now be described with reference to FIG. 1. This example of the tilt sensor consists of a combination of an LED 101 provided to face the recording plane of an optical disc 100, a two-piece photodetector 102 and a subtracter 103. The LED 101 emits an LED light to the recording plane of the optical disc 100, the light reflected by the recording plane of the optical disc 100 is received by the photodetector 102, the difference between the light-reception signals from the respective two areas of the two-piece photodetector is obtained through the subtracter 103, and the thus-obtained difference signal is outputted as a tilt-error signal indicating the tilt of the optical disc 100.
However, in this example, because the tilt sensor is provided completely separately from the optical-pickup device, an extra setting space is needed, thereby, miniaturization of the entire optical-disc apparatus is obstructed, and, also, the cost of the apparatus increases. Further, it is necessary to set the LED 101 in a manner in which the optical axis of the LED 101 is accurately parallel to the optical axis of the laser light of the optical-pickup device. Therefore, the adjustment work at the time of assembly is troublesome. Furthermore, because the tilt sensor shown in FIG. 1 is located distantly from the objective lens, the accuracy in detection of the relative tilt between the optical disc 100 and the objective lens performed through the tilt sensor is not high. Furthermore, generally speaking, the tilt of the objective lens varies due to focusing and tracking. In such a case, it is not possible to detect the tilt of the objective lens accurately.
For example, Japanese Laid-Open Patent Application No. 9-147395 discloses an optical-pickup device in which these problems are solved. This optical-pickup device will now be described with reference to FIGS. 2 and 3. This optical-pickup device includes a laser diode 110 which is a light source. This device further includes a polarization beam splitter 113 which transmits the light emitted by the laser diode 110 as it is, and, thus, causes the light to travel to an optical disc 111. The polarization beam splitter 113 also reflects light reflected by the optical disc 111 through the polarization plane thereof, and, thus, causes the light to travel to a four-piece photodetector 112. The device further includes a collimator lens 114 which collimates the light, emitted by the laser diode 110. The device further includes a quarter-wave plate 115 which rotates the vibration plane of the light, which the plate 115 transmits, by a xc2xc wavelength. The device further includes a hologram element 116 which disperses the parallel light, provided from the quarter-wave plate 115, into the 0-th-order light (non-diffracted light) and the first-order light. The device further includes an objective lens 117, which is formed so as to be integral with the hologram element 116, and which has a plurality of focuses so as to adapt to variation of the thickness of the substrate of the optical disc. A multiple-focus lens 118 is formed as a result of combining the objective lens 117 and the hologram element 116. The device further includes a multiple lens 119, acting as astigmatism means, provided in front of the photodetector 112. The multiple-focus lens 118 disperses incident light into a plurality of beams of light. A beam L0 (or L1) of the plurality of beams of light, which beam is focused on the recording plane of the optical disc 111, is reflected thereby, and the thus-obtained light is received by the photodetector 112 through the multiple lens 119. The thus-received light is used as a signal for reproducing information recorded on the optical disc 111.
In addition to this basic arrangement, two light-receiving elements 121 and 122 are provided on both sides of the photodetector 112, in a direction corresponding to the radial direction of the optical disc 111, as shown in FIG. 3. The difference between the output signals of these light-receiving elements 121 and 122 is obtained through a subtracter 123. The thus-obtained difference is used as a tilt-error signal.
However, in the case of the tilt-detecting method shown in FIGS. 2 and 3, because the laser light emitted by the laser diode 110 is modulated at the time of a recording operation, it is not possible to obtain a stable tilt-error signal. Further, the extra light-receiving elements 121 and 122 are needed. Therefore, the arrangement is complicated, and, also, cost reduction and miniaturization of the device are obstructed.
Further, when an optical-axis deviation exists between the ideal optical axis and the optical axis of the objective lens at the time of tracking, the offset due to the optical-axis deviation is included in the tilt signal. However, it is not possible to determine whether this offset develops due to the optical-axis deviation or the tilt. Therefore, in a case where an optical system is such that the optical-axis deviation is large, a countermeasure such as to provide a member for detecting the optical-axis deviation is needed.
An object of the present invention is to provide an optical-pickup device and a tilt-detecting method in which, basically, it is not necessary to provide an extra member for detecting the tilt, and, also, the tilt can be always detected even during a recording/reproducing operation.
Another object of the present invention is to provide an optical-pickup device in which the tilt can be accurately detected without being affected by the offset due to the optical-axis deviation.
An optical-pickup device according to the present invention, comprises:
a plurality of light sources;
an objective lens for converging light from the plurality of light sources on an optical disc; and
at least one light-receiving element for receiving light reflected by the optical disc,
wherein a light source of the plurality of light sources, which light source is one not used for recording/reproducing, is used for detecting relative tilt between the optical disc and the objective lens.
In this arrangement, in the optical-pickup device having the plurality of light sources, at the time of recording/reproducing, one of the light sources, which one is one not used for the recording/reproducing, is used for the tilt detection. As a result, the objective lens which is used for recording/reproducing can also be used for the tilt detection in common. Therefore, it is not necessary to additionally provide a special tilt-detecting member, and, also, it is possible to accurately perform the tilt detection. Furthermore, it is possible to perform the tilt detection in real time even during a recording/reproducing operation. In particular, when one of the light sources is used and a recording/reproducing operation is performed, the light emitted by another one of the light sources does not focus on the optical disc, that is, the emitted light is in a defocus condition. However, a focusing operation is always performed on the side of the one of the light sources used for recording/reproducing. As a result, the focus-deviation amount on the side of the one of the light sources used for the tilt detection is always constant. Therefore, the defocus condition on the side of the one of the light sources used for the tilt detection is in a stable defocus condition. Accordingly, it is possible to perform stable, accurate tilt detection even in the defocus condition.
The optical-pickup device can perform recording/reproducing on any one of a plurality of types of optical discs, the thicknesses of substrates of the plurality of types of optical discs being different from each other.
Therefore, it is possible to perform the tilt detection for the plurality of types of optical discs, the thicknesses of substrates of which are different from each other.
An optical-pickup device according to another aspect of the present invention, comprises:
an objective lens for converging light, emitted from a light source which is used for tilt detection, to an optical disc; and
an objective-lens actuator such that no optical-axis deviation develops between the ideal optical axis and the optical axis of the objective lens at a time of tracking when said object-lens actuator is used.
In this arrangement, the signal developing due to optical-axis deviation is not included in the tilt signal. Therefore, it is not necessary to provide an optical-axis deviation detecting member, and it is possible to perform the tilt detection accurately. In this arrangement, the light source used for the tilt detection may be the light source which is also for recording/reproducing in common, or may be any one of the plurality of light sources as described above.
The at least one light-receiving element may comprise a plurality of light-receiving elements for the plurality of light sources, respectively; and
each light-receiving element is used for detecting an information signal and a servo signal based on the light reflected by the optical disc, and the same light-receiving element is also used for detecting a tilt signal based on the light reflected by the optical disc.
In this arrangement, it is not necessary to additionally provide a special light-receiving element for the tilt detection. Thereby, it is possible to perform miniaturization of the device, and, also, to reduce the cost of the device.
The at least one light-receiving element may comprise a single light-receiving element for the plurality of light sources; and
the light-receiving element is used for detecting an information signal and a servo signal based on the light reflected by the optical disc, and the same light-receiving element is also used for detecting a tilt signal based on the light reflected by the optical disc.
In this arrangement, the single light-receiving element is used for the plurality of light sources in common. Thereby, it is possible to perform further miniaturization of the device, and, also, to further reduce the cost of the device.
A tilt-detecting method according to the present invention, comprises the steps of:
a) using any one of a plurality of light sources as a light source for detecting a relative tilt between an optical disc and an objective lens; and
b) causing, at a time of tilt detection, the light source to emit light obtained as a result of light intensity modulation with a waveform including an alternating-current component, the basic frequency of the waveform being fixed.
In this method, even in an arrangement in which a single light-receiving element receives light emitted by the plurality of light sources and reflected by the optical disc, it is not necessary to additionally provide a special light-receiving element for the tilt detection because it is possible to use the single light-receiving element for recording/reproducing and also for the tilt detection in common. Accordingly, it is possible to perform the tilt detection through the miniature, inexpensive arrangement.
The above-mentioned waveform may approximate a rectangular wave.
The waveform may be selected so that frequency components of the waveform are out of a control band so that a focusing-and-tracking servo system does not respond to the frequency components, and the frequency components include none or a few of the frequency components of a recording signal, have or little influence on increase of jitter in a reproduced signal, or include none or a few of frequency components of various signals generated based on information formed on the optical disc.
In this method, the intensity-modulation waveform is selected so that the thus-intensity-modulated laser light for the tilt detection does not adversely affect the servo control nor the recording/reproducing operation. As a result, it is possible to perform the tilt-detecting operation in real time.
A signal which includes no direct-current component may be used for a tilt-detecting calculation.
At a beginning of the tilt detection, the level of the light emitted by the light source for the tilt detection may be caused to rise in a manner in which the intensity of the emitted light increases gradually, and, also, the amplitude increases gradually so as to become a fixed amplitude, and, at an end of the tilt detection, the level of the laser light emitted by the light source for the tilt detection may be caused to decay in a manner in which the intensity of the emitted light decreases gradually, and, also, the amplitude decreases gradually from the fixed amplitude.
In this method, even in a condition in which a plurality of light sources are adjacently located, such as a case where a plurality of light source are contained in one package, it is possible to prevent the light sources from being deteriorated.
A tilt-detecting operation may be performed intermittently.
In this method, even in a condition in which a plurality of light sources are adjacently located, such as a case where a plurality of light source are contained in one package, it is possible to reduce the influence (noise) on the servo signal and reproduced signal, which influence (noise) occurs at the time of the rising and the time of decaying of the tilt-detecting signal.
In an operation mode in which a tilt-detecting operation cannot be performed, tilt correction may performed using tilt data which was detected in a tilt-detecting operation performed before the beginning of this operation mode.
In this method, in an operation mode in which a tilt-detecting operation cannot be performed, such as a seeking-operation mode, because influence developing due to change in tilt is small, it is possible to perform a proper tilt correction using tilt data detected when the optical disc was loaded in the optical device.
An offset of a focus-error signal or a tracking-error signal generated due to the tilt-detection light at the time of tilt detection may be removed based on detected tilt data.
In this method, the offset developing due to the tilt-detecting light and included in the focus-error signal or tracking-error signal obtained based on the light reflected by the recording plane of the optical disc is removed based on the detected tilt data. Thereby, it is possible to obtain the correct focus-error signal or tracking-error signal, and to perform proper focusing or tracking control.
An S-shape tracking-error or focus-error signal may be detected in a condition in which the light source for the tilt detection is in its turned-off state, then, the S-shape tracking-error or focus-error signal may be detected in a condition in which the light source for the tilt detection is driven so that the light source emits the light obtained as a result of intensity modulation with the waveform, the difference (axe2x88x92b) between the S-shape tracking-error or focus-error signals detected in these different conditions may be calculated, the level xe2x80x98cxe2x80x99 of the mean direct-current signal of the tilt-detection signal may be detected, the mean direct-current signal may be inputted to a gain-adjustment circuit, the gain of which is set to be (axe2x88x92b)/c, and the offset component of the focus-error or tracking-error signal may be removed using the output of the gain-adjustment circuit, the output of which is caused to be equal to the difference (axe2x88x92b).
An optical-pickup device, according to another aspect of the present invention, which can record information on any one of a plurality of types of optical recording media, the thicknesses of the substrates of the plurality of types of optical recording media being different from each other, and wavelengths used for performing recording/reproducing on the plurality of types of optical recording media being different from each other, and can reproduce information recorded on the one of the plurality of types of optical recording media, the device comprising:
a semiconductor laser which emits laser light of a first wavelength;
a wavelength-converting element which produces laser light of a second wavelength which is half of the first wavelength;
a converging optical system which can focus the laser light of a selected wavelength on the information recording plane of the one of the plurality of types of optical recording media, the selected wavelength being one of the first and second wavelengths corresponding to the one of the plurality of types of optical recording media;
a light-path splitting element which splits the light path of the laser light of the first wavelength and the laser light of the second wavelength into separate light paths for the respective first and second wavelengths;
a first detector which detects the reflected laser light of the first wavelength; and
a second detector which detects the reflected laser light of the second wavelength,
wherein either one of the laser light of the first wavelength and the laser light of the second wavelength is used for performing recording/reproducing of information on the one of the plurality of types of optical recording media, and, also the other one is used for tilt detection for detecting the relative tilt between the information recording plane of the one of the plurality of type of optical recording media and an objective lens of the converging optical system.
In this arrangement, in the optical-pickup device which can perform recording/reproducing on any one of the optical recording medium for which the laser light of the first wavelength is used and the optical recording medium for which the laser light of the second wavelength is used, either one of the laser light of the first wavelength and the laser light of the second wavelength is used for performing recording/reproducing of information on the one of the plurality of types of optical recording media, and, also, the other one is used for tilt detection for detecting the relative tilt between the information recording plane of the one of the plurality of types of optical recording media and an objective lens of the converging optical system. Therefore, stable, real-time tilt detection (tilt detection using the laser light which is not focused on the optical recording medium while the other laser light is focused on the optical recording medium) can be performed using the laser light which is not used for recording/reproducing. Further, the laser light of the first wavelength and the laser light of the second waveform, reflected by the optical recording medium, are stably detected by the different detectors, respectively. Furthermore, because the arrangement is not complicated, it is possible to miniaturize and reduce the cost of the optical-pickup device. Furthermore, because the objective lens which is used for recording/reproducing is also used for the tilt detection in common, it is possible to accurately perform the tilt detection without additionally providing a special tilt-detecting member.
The light-path splitting element may be provided in front of each of the first and second detectors.
In this arrangement, as a result of providing the light-path splitting element in proximity to the detectors, it is possible to detect the laser light of the first wavelength and the laser light of the second waveform, reflected by the optical recording medium, using the stable signals.
The converging optical system may comprise a first objective lens for focusing the laser light of the first wavelength on the corresponding one of the plurality of types of optical recording media and a second objective lens for focusing the laser light of the second wavelength on the corresponding one of the plurality of types of optical recording media;
one of the first and second objective lenses may be selected to be used for performing recording/reproducing of information on one of the plurality of types of optical recording media, the one of the plurality of types of optical recording media being one on which recording/reproducing of information is currently performed, the one of the first and second objective lenses being one corresponding to the one of the plurality of types of optical recording media; and
the one of the first and second objective lens may be inserted into the light path of the laser light.
In this arrangement, the objective lenses are provided for the two wavelengths, and the proper one is selected therefrom for the type of the optical recording medium. Thereby, it is possible to detect the stable signals by preventing development of an aberration due to the difference in the thickness of the substrate of the optical recording medium and so on, and to detect the laser light of the first wavelength and the laser light of the second waveform, reflected by the optical recording medium, using the stable signals through the different detectors, respectively.
The converging optical system may comprise the objective lens for focusing the laser light of the second wavelength on the corresponding one of the plurality of types of optical recording media and a numerical-aperture limiting aperture for limiting the numerical aperture of the objective lens for the laser light of the first wavelength so as to focus the laser light of the first wavelength on the corresponding one of the plurality of types of optical recording media; and
the numerical-aperture limiting aperture may be provided in the light path of the laser light in front of the objective lens.
In this arrangement, the objective lens and numerical-aperture limiting aperture are provided for the two wavelengths. Thereby, it is possible to detect the stable signals by preventing development of the aberration due to the difference in the thickness of the substrate of the optical recording medium and so on, to prevent the arrangement from being complicated due to addition of a lens, and to detect the laser light of the first wavelength and the laser light of the second waveform, reflected by the optical recording medium, using the stable signals, through the different detectors, respectively.
An optical-pickup device, according to another aspect of the present invention, which can record information on any one of a plurality of types of optical recording media, the thicknesses of the substrates of the plurality of types of optical recording media being different from each other, and wavelengths used for performing recording/reproducing on the plurality of types of optical recording media being different from each other, and can reproduce information recorded on the one of the plurality of types of optical recording media, the device comprising:
a first semiconductor laser which emits laser light of a first wavelength;
a wavelength-converting element which produces laser light of a second wavelength which is half of the first wavelength;
a second semiconductor laser which emits laser light of a third wavelength which is different from the first wavelength and also is different from the second wavelength;
a light-path synthesis element which causes the light path of the laser light of the third wavelength to become the same as the light path of the laser light of the first wavelength and the laser light of the second laser light;
a converging optical system which can focus the laser light of a selected wavelength on an information recording plane of the one of the plurality of types of optical recording media, the selected wavelength being one of the first and second wavelengths corresponding to the one of the plurality of types of optical recording media;
a detector which can detect at least any of the reflected laser light of the first wavelength, the reflected laser light of the second wavelength and the reflected laser light of the third wavelength,
wherein any one of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength is used for performing recording/reproducing of information on the one of the plurality of types of optical recording media, and, also at least one of the other two of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength is used for tilt detection for detecting a relative tilt between the information recording plane of the one of the plurality of types of optical recording media and an objective lens of the converging optical system.
In this arrangement, in the optical-pickup device which can perform recording/reproducing on any one of the optical recording medium for which the laser light of the first wavelength is used, the optical recording medium for which the laser light of the second wavelength is used and the optical recording medium for which the laser light of the third wavelength is used, any one of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength is used for performing recording/reproducing of information on the one of the plurality of type of optical recording media, and, also, another one is used for tilt detection for detecting the relative tilt between the information recording plane of the one of the plurality of types of optical recording media and an objective lens of the converging optical system. Therefore, stable, real-time tilt detection (tilt detection using the laser light which is not focused on the optical recording medium while the other laser light is focused on the optical recording medium) can be performed using the laser light which is not used for recording/reproducing. Further, because at least any of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength, reflected by the optical recording medium, are detected by the same single detector, it is possible to miniaturize and to reduce the cost of the optical-pickup device. Furthermore, because the objective lens which is used for recording/reproducing is also used for the tilt detection in common, it is possible to accurately perform the tilt detection without additionally providing a special tilt-detecting member.
The optical-pickup device may further comprise at least two wavelength-selecting elements which selectively transmit a first combination of two of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength and a second combination of two of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength, respectively.
In this arrangement, by providing the at least two wavelength-selecting elements which selectively transmit a first combination of two of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength and a second combination of two of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength, respectively, it is possible to prevent the laser light of the wavelength which is not used for the recording/reproducing nor the tilt detection from being incident on the detector.
An optical-pickup device, according to another aspect of the present invention, which can record information on any one of a plurality of types of optical recording media, the thicknesses of the substrates of the plurality of types of optical recording media being different from each other, and wavelengths used for performing recording/reproducing on the plurality of types of optical recording media being different from each other, and can reproduce information recorded on the one of the plurality of types of optical recording media, the device comprising:
a first semiconductor laser which emits laser light of a first wavelength;
a wavelength-converting element which produces laser light of a second wavelength which is half of the first wavelength;
a second semiconductor laser which emits laser light of a third wavelength which is different from the first wavelength and also is different from the second wavelength;
a light-path synthesis element which causes the light path of the laser light of the third wavelength to become the same as the light path of the laser light of the first wavelength and the laser light of the second wavelength;
a converging optical system which can focus the laser light of a selected wavelength on an information recording plane of the one of the plurality of types of optical recording media, the selected wavelength being one of the first and second wavelengths corresponding to the one of the plurality of types of optical recording media;
a light-path splitting element which splits the light path of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength into separate light paths for the respective first, second and third wavelengths;
a first detector which detects the reflected laser light of the first wavelength;
a second detector which detects the reflected laser light of the second wavelength; and
a third detector which detects the reflected laser light of the third wavelength,
wherein any one of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength is used for performing recording/reproducing of information on the one of the plurality of types of optical recording media, and, also, at least one of the other two of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength is used for tilt detection for detecting a relative tilt between the information recording plane of the one of the plurality of types of optical recording media and an objective lens of the converging optical system.
In this arrangement, in the optical-pickup device which can perform recording/reproducing on any one of the optical recording medium for which the laser light of the first wavelength is used, the optical recording medium for which the laser light of the second wavelength is used and the optical recording medium for which the laser light of the third wavelength is used, any one of the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength is used for performing recording/reproducing of information on the one of the plurality of types of optical recording media, and, also, the other one is used for tilt detection for detecting the relative tilt between the information recording plane of the one of the plurality of types of optical recording media and an objective lens of the converging optical system. Therefore, stable, real-time tilt detection (tilt detection using the laser light which is not focused on the optical recording medium while the other laser light is focused on the optical recording medium) can be performed using the laser light which is not used for recording/reproducing. Further, the laser light of the first wavelength, the laser light of the second waveform and the laser light of the third wavelength, reflected by the optical recording medium, are stably detected by the different detectors, respectively. Furthermore, because the arrangement is not complicated, it is possible to miniaturize and reduce the cost of the optical-pickup device. Furthermore, because the objective lens which is used for recording/reproducing is also used for the tilt detection in common, it is possible to accurately perform the tilt detection without additionally providing a special tilt-detecting member.
The light-path splitting element may be provided in front of each of the first, second and third detectors.
In this arrangement, as a result of providing the light-path splitting element in proximity to the detectors, it is possible to detect the laser light of the first wavelength, the laser light of the second wavelength and laser light of the third wavelength, reflected by the optical recording medium, using the stable signals.
The converging optical system may comprise a first objective lens for focusing the laser light of the first wavelength on the corresponding one of the plurality of types of optical recording media, a second objective lens for focusing the laser light of the second wavelength on the corresponding one of the plurality of types of optical recording media and a third objective lens for focusing the laser light of the third wavelength on the corresponding one of the plurality of types of optical recording media;
one of the first, second and third objective lenses may be selected to be used for performing recording/reproducing of information on one of the plurality of types of optical recording media, the one of the plurality of types of optical recording media being one on which recording/reproducing of information is currently performed, the one of the first, second and third objective lens being one corresponding to the one of the plurality of types of optical recording media; and
the one of the first, second and third objective lens may be inserted into the light path of the laser light.
In this arrangement, the objective lenses are provided for the three wavelengths, respectively, and the proper one is selected therefrom for the type of the optical recording medium. Thereby, it is possible to detect the stable signals by preventing development of the aberration developing due to the difference in the thickness of the substrate of the optical recording medium and so on, and to detect the laser light of the first wavelength, the laser light of the second wavelength and the laser light of the third wavelength, reflected by the optical recording medium, using the stable signals, through the different detectors, respectively.
The converging optical system may comprise the objective lens for focusing the laser light of the second wavelength on the corresponding one of the plurality of types of optical recording media and a numerical-aperture limiting aperture for limiting the numerical aperture of the objective lens for the laser light of the first wavelength and the laser light of the third wavelength so as to focus the laser light of the first wavelength on the corresponding one of the plurality of types of optical recording media and focus the laser light of the third wavelength on the corresponding one of the plurality of types of optical recording media; and
the numerical-aperture limiting aperture may be provided in the light path of the laser light in front of the objective lens.
In this arrangement, the objective lens and numerical-aperture limiting aperture are provided for the three wavelengths. Thereby, it is possible to detect the stable signals by preventing development of the aberration developing due to the difference in the thickness of the substrate of the optical recording medium and so on, to prevent the arrangement from being complicated due to addition of a lens, and to detect the laser light of the first wavelength and the laser light of the second wavelength, reflected by the optical recording medium, using the stable signals, through the different detectors, respectively.
When recording/reproducing is performed on one of the plurality of types of optical recording media, the one of the plurality of types of optical recording media being one corresponding to the laser light of the first wavelength, the wavelength-converting element may not cause the phases of the components of the laser light of the second wavelength to match with each other, so that the wavelength-converting element does not emit the laser light of the second wavelength.
In this arrangement, when recording/reproducing is performed on the one of the plurality of types of optical recording media, the one of the plurality of types of optical recording media being one corresponding to the laser light of the first wavelength, only the laser light of the first wavelength is caused to be emitted from the wavelength-converting element. Thereby, at this time, it is possible to use the laser light of the first wavelength at high efficiency. In a case where the wavelength converting element is a second-harmonic generating element in which a quasi phase matching is used, when the quasi phase matching is not performed (when blue laser light is not emitted), it is possible to provide a sufficient amount of infrared laser light. Thereby, it is possible to improve the light use efficiency at the time of recording/reproducing performed on the CD.
The light-path splitting element may comprise a dichroic mirror.
In this arrangement, because the arrangement of the optical-pickup device is not complicated, it is possible to miniaturize and to reduce the cost of the optical-pickup device.
The light-path splitting element may comprise a wavelength selecting hologram.
In this arrangement, because the arrangement of the optical-pickup device is not complicated, it is possible to miniaturize and to reduce the cost of the optical-pickup device.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.